Modified Christie-Atkins-Munch-Petersen (CAMP) test for direct identification of hemolytic and nonhemolytic group B streptococci on primary plating.

A primary plating medium, using sheep blood agar with preformed zones of cell-free staphylococcal beta-hemolysin, was used for direct identification of both hemolytic and nonhemolytic group B streptococci by the direct elicitation of the Christie-Atkins-Munch-Petersen (CAMP) reaction. A positive CAMP reaction consisted of a semilunar-shaped area or circle of complete hemolysis of sheep erythrocytes and occurred only when colonies of group B streptococci developed along the periphery of the preformed zone of staphylococcal beta-hemolysin. Of 104 simulated specimens containing group B streptococci in combination with a variety of microbial species and of 85 vaginal specimens examined, direct recognition of group B streptococci was possible in 64 (61.5%) simulated specimens and in 12 (100%) vaginal cultures. Group B streptococcal colonies not developing along the active edge of staphylococcal beta-hemolysin were still identified by subculture. Of particular value was the facilitated recognition of colonies of nonhemolytic group B streptococcal strains and of hemolytic group B streptococci few in number or overgrown by other microbial species.